1. Field of the Invention
The present invention relates to the fabrication of integrated circuits. More particularly, the invention relates to a process for depositing dielectric layers on a substrate and the structures formed by the dielectric layer.
2. Background of the Invention
Semiconductor device geometries have dramatically decreased in size since such devices were first introduced several decades ago. Since then, integrated circuits have generally followed the two year/half-size rule (often called Moore""s Law), which means that the number of devices that will fit on a chip doubles every two years. Today""s fabrication plants are routinely producing devices having 0.13 xcexcm and even 0.1 xcexcm feature sizes, and tomorrow""s plants soon will be producing devices having even smaller geometries.
In order to further reduce the size of devices on integrated circuits, it has become necessary to use conductive materials having low resistivity and to use insulators having low dielectric constants (k less than 4.0) to reduce the capacitive coupling between adjacent metal lines. One such low k material is spin-on glass, such as un-doped silicon glass (USG) or fluorine-doped silicon glass (FSG), which can be deposited as a gap fill layer in a semiconductor manufacturing process. Other examples of low k materials include silicon dioxide and polytetrafluoroethylene which are all commercially available. However, the continued reduction in device geometries has generated a demand for films having even lower k values.
Rose et al. (U.S. Pat. No. 6,068,884) discloses a method of depositing an insulator wherein a cyclic organosilicon compound, octamethylcylcotetrasiloxane (OMCTS), is partially fragmented to form both cyclic and chain structures in the deposited film. However, partially fragmenting cyclic precursors is difficult to control. Therefore, there is a need for a controllable process for making low dielectric constant materials that would improve the speed and efficiency of devices on integrated circuits.
The present invention provides a method for depositing a low dielectric constant film having a dielectric constant of about 3.0 or less, preferably about 2.5 or less. In one aspect, a cyclic organosilicon compound and an aliphatic organosilicon compound are reacted with an oxidizing gas at conditions sufficient to deposit a low dielectric constant film on the semiconductor substrate. The cyclic organosilicon compound comprises at least one silicon-carbon bond. The aliphatic organosilicon compound comprises a silicon-hydrogen bond or a silicon-oxygen bond. A sufficient amount of the aliphatic organosilicon compound is added to the cyclic organosilicon compound to provide a dielectric constant at least 5% lower than a dielectric constant obtained by omitting the aliphatic organosilicon compound.
In another aspect, a method for depositing a low dielectric constant film comprises flowing a cyclic organosilicon compound and an aliphatic organosilicon compound into a reaction zone at a volume ratio between about 1:4 and about 4:1, and reacting the compounds with an oxidizing gas while applying RF power to deposit a film having a dielectric constant of about 3 or less, preferably about 2.5 or less. The cyclic organosilicon compound comprises at least three silicon atoms and from one to two alkyl groups bonded to each silicon atom. The aliphatic organosilicon compound comprises at least one hydrogen or at least one alkoxy group bonded to at least one silicon atom. In another aspect, both the cyclic organosilicon compound and the aliphatic organosilicon compound comprise at least one silicon-hydrogen bond.